From the Store description:
Get your intranet in your pocket with the SharePoint mobile app. With easy on-the-go access, the SharePoint mobile app helps keep your work moving forward by providing quick access to your team sites, organization portals and resources, and the people you work with. You can see site activities, get quick access to recent and popular files, and view and arrange lists on your team sites.
• Sign in to your SharePoint Online sites. You can add multiple accounts, and easily switch between them.
• Quickly find your sites. Check out the Sites tab, to see the sites you frequently visit and the sites you follow. Tap on a team site to dive into it. See site activity, navigate using the familiar quick launch navigation, easily follow or share the site, and work with your lists.
• Check out recent and popular files. In a team site, get to your recent or popular files quickly to view or share them, and have full access to your document libraries using the new integration with the OneDrive app. Edit your files easily using Office Mobile apps like Word, Excel, PowerPoint, and OneNote.
• Use the Links tab to find promoted links for your organization. Curated by your SharePoint admin for all employees, these links get you to the organizational resources and sites that you care about.
• Search. Enterprise Search is available throughout the app and results are organized into sites, files and people.
• Find and browse for people you work with. Tap on a user to get to their contact card and to see who they work with and what they are working on.
Here's the app in action in a couple of promo screenshots - note that it's a full UWP app and Continuum-friendly:
You can grab SharePoint here in the Store. It looks pretty barebones to me, as an outsider - I do get the impression that Microsoft Teams is where the Office 365 teamwork and sharing action is these days. Yes, the two systems aren't quite the same, but there's quite a bit of overlap.